Electrically small spiral antenna tunable over a wide band



Dec. 17, 1968 R. c. FENWICK 3,417,403 ELECTRICALLY SMALL SPIRAL ANTENNA TUNABLE OVER A WIDE BAND Filed Nov. 18, 1965 a/ Y H, A; /6 /0 a2 -74 7777777, F77777777777777777-7777r Vii; 77

777777777; FIG I m FIG 2 A 88 U as /89 H J 1 ar FIG 3 TAKE-UP REEL (s fr e Lg 'o) (D'ELECTRIC) TAKE-UP REEL CONDUCTOR (SPRING LOADED) POWER CONNECTOR g'g'g 2/ EgMw 69 $HEEE FOR FIG 4 INVENTOR. ANTENNA RICHARD C FENWICK ATTORNEY United States Patent 3,417 403 ELECTRICALLY SMAIjL SPIRAL ANTENNA TUNABLE OVER A WIDE BAND Richard C. Fenwick, Richardson, Tex., assignor to Collins Radio Company, Cedar Rapids, Iowa, a corporation of owa Filed Nov. 18, 1965, Ser. No. 508,482 4 Claims. (Cl. 343877) ABSTRACT OF THE DISCLOSURE A tunable electrically-small antenna which minimizes spacial requirements may be formed of a solenoid winding operating at or near first resonance, the winding having a length corresponding to one half the wavelength of an energizing signal. One end of the winding is grounded and the other end is fed with the sense of the winding being reversed at the center. Tuning may be accomplished by varying the number of turns on a dielectric drum upon which the winding is formed.

This invention relates in general to antennas and in particular to an electrically small antenna tunable over a wide band.

It is an object of this invention to provide a compact and simple antenna capable of being tuned over a Wide frequency range.

Another object of this invention is to provide an improved, efficient antenna.

A feature of this invention is found in the provision for tunable antenna which consists of .a winding Wound about a core. The direction of winding is reversed at the center of the core and one end is connected to ground and the other end to a suitable driving means.

Further objects, features, and advantages of this invention will become apparent from the following description and claims when read in view of the accompanying drawings, in which:

FIGURE 1 is a schematic illustration of the antenna;

FIGURE 2 illustrates a modification of the antenna;

FIGURE 3 illustrates a modification of the invention; and

FIGURE 4 illustrates a mechanical arrangement for tuning the antenna.

FIGURE 1 illustrates a ground plane designated generally as and a dielectric drum 11 which is rotatably supported above the ground plane. A solenoid winding 12 consists of a first section 13 which has one end connected to the ground and is wound about the dielectric drum in a first direction for substantially half the length of the drum. A second half 14 of the solenoid winding is wound about the drum in a direction opposite to the first half of the winding and has one end connected to a feed conductor 16. Such an antenna consists of a solenoid winding over a ground plane with one end grounded and the other end fed and the sense of the winding is reversed at the center. The winding operates at or near first resonance and consists 'of a half wave winding. Tuning may be done by varying the number of turns on the dielectric drum. For example, the structure of FIGURE 4 illustrates a manner in which this may be accomplished. A base member 21 supports a pair of plates 22. and 23 in which a shaft 24 is rotatably supported. A pulley 26 is mounted on shaft 24 and is connected to the output shaft of a motor 27 which is supported by standoff 28 which is attached to the base member. A second shaft is also mounted between plates 22 and 23 and has a pulley 31 attached to one end. A belt 32 passes over pulleys 26 and 31. A portion 33 of shaft 29 is threaded and carries internally threaded carriage members 34 and 36. A slotted guide 37 extends from plates 22 and 23 and engages the threaded carriages 34 3,417,403 Patented Dec. 17, 1968 and 36 to allow them to move longitudinally as shaft 29 is rotated, but prevents them from rotating. The carriage 34 carries a shaft 37 upon which a pulley 38 is mounted. Likewise, the carriage 36 carries a shaft 39 on which a pulley 41 is mounted.

A dielectric tape drum 42 is mounted on the shaft 24 between plates 22 and 23 and is formed with grooves 43 into which a flexible tape conductor 44 can be received. The conductor is formed with a connecting section 46 which joins the two half windings 47 and 48 at the center of the drum 42. The outer ends 49 and 51 of the half windings 47 and 48 pass over the pulleys 38 and 41 respectively. End 49 then passes over pulley 52 which is rotatably supported from plate 22 by shaft 53 and passes to a spring loaded take-up reel 54 supported by standoffs 56 from plate 22. An opening 57 in reel 54 allows shaft 24 to extend through the reel. The other end 51 passes from pulley 41 over a pulley 55 supported by shaft 58 from plate 23 and to a second spring loaded take-up reel 59 which is supported by standotfs 61 from plate 23. The take-up reels 54 and 59 consist of outer rotatable portions 62 and 63 which hold surplus conducting tape 44 and stationary portions 64 and 65. A spring means, not shown, bias the outer take-up portions 62 and 63 of the reels so that the reels hold and maintain tension on the tape 44 to take up excess tape when the drum 42 is rotated in a first direction, but are capable of allowing additional tape to be fed onto the drum when the drum is rotated in the opposite direction. The tape may be silver-plated beryllium copper.

The motor 27 rotates the drum 42 in either direction and simultaneously the carriers 34 and 36 are driven by the shaft 29 to feed the tape 44 into suitable grooves on the tape drum. A wiper 66 engages one end of the tape 44 and is connected to the ground plane. A second Wiper 67 engages the other end of tape 44 and is connected to a feed line 68 which may be connected to a suitable generator 69. Power lines 71 and 72 are connected to the motor through a reversing switch S to tune the antenna. As motor 27 rotates shafts 24 and 29, the tape is laid into or taken out of grooves 43 of drum 42 to tune the antenna.

FIGURE 2 illustrates a modification of the invention wherein a pair of dielectric drums 73 and 74 are mounted adjacent to each other above a ground plane 76. A first winding 77 has one end 78 connected to ground and is wound about the first drum '73 in a first direction. A second winding 79 is wound about the second drum 74 in a direction opposite to winding 77 and has its first end 81 of the second winding connected to a suitable feed conductor 82. The second ends 83 and 84 of the windings are connected together.

FIGURE 3 illustrates a further modification in which a pair of dielectric cores 86 and 87 are wound with windings 88 and 89.

These windings are formed of two half windings which pass about the cores in opposite directions. The ends 91 and 92 of windings are connected together and a generator 93 is connected to the other ends 94 and 96. The cores 86 and 87 are spaced adjacent each other and parallel to each other to produce a tunable balanced antenna.

The reversal of the direction of the winding at the center of the core causes a current phase reversal at midwinding and maintains positive mutual impedances throughout the structure thus requiring less winding than expected.

It is seen that this invention provides a new and novel antenna and although it has been described with respect to particular embodiments thereof, it is not to be so limited, as changes and modifications may be made therein which are within the spirit and scope of the invention as defined by the appended claims.

I claim:

1. An antenna comprising a cylindrical coil form rotatably supported, flexible tape of electrical conducting material attached to the center of the coil form and the ends wound in opposite directions around the coil form so that as the coil form is rotated in a first direction the flexible tape is laid on the coil form simultaneously and as the coil form is rotated in the other direction the flexible tape is removed from the coil form, a pair of spring tensioned reels attached to the ends of the flexible tape to play out or take it up, a pair of lay-on guides movable relative to the coil form over which the flexible tape passes to lay-on or take 01f the tape, driving means attached to the coil form and the lay-on guides to move them simultaneously, said lay-on guides consisting of pulleys attached to carriage means, a threaded shaft attached to the carriage means and supported for rotary motion and means for allowing the carriage means for moving longitudinally of the coil form but not transversely.

2. In apparatus according to claim 1, a first electrical lead connecting one end of the flexible tape to a ground plane and a second electrical lead connecting the other end of the flexible tape to a feed point.

3. An antenna comprising a coil form mounted with its longitudinal axis parallel to a ground plane, a winding wound about the coil form with one half of the winding wound about the coil form in one direction and the other half wound about the form in the other direction at the other end of the coil form, a first electrical lead connecting one end of one half of the winding to the ground plane, the other end of the one half of the winding connected to the first end of the other half of the winding and the second end of the other half of the winding connecting to' a feed conductor, said winding having a length corresponding to one half wavelength of a signal applied between said feed conductor and said ground plane.

4. An antenna comprising, a pair of coil forms the longitudinal axes of which are mounted in a parallel-spaced relationship with respect to a ground plane, a conductor wound about both coil forms and wound in an opposite direction on each coil form, first juxtaposed ends of the windings on the coil forms connected together, the second end of one of the windings connecting to said ground plane, the second end of the other winding connected to a feed conductor, said winding having a length corresponding to one half wavelength of a signal applied between said first conductor and said ground plane.

References Cited UNITED STATES PATENTS 1,684,009 9/1928 Brown 343895 2,452,679 11/1948 Ramsden 336--15 2,482,767 9/1949 Hansen 343895 2,282,964 5/1961 Bresk et al. 343-895 3,226,725 12/1965 Ritchie et al. 343750 3,085,215 4/1963 Shepherd 343750 ELI LIEBERMAN, Primary Examiner.

, US. Cl. X.R. 33615; 343 s9s 

